Americans enjoy a handful of federal holidays every year, and most of them have relatively straightforward definitions. Veterans Day honors military service. The Fourth of July acknowledges the country’s independence. But Presidents Day is something of a mystery.

Contrary to popular belief, it’s not a catch-all holiday meant to celebrate the presidents. In fact, it doesn’t legally exist at all. It’s technically known as Washington’s Birthday at the federal level, and Abraham Lincoln, presumed to be part of the honor, doesn’t have anything to do with it.

Beginning in 1968, Congress took a second look at federal holidays with the Uniform Monday Holidays Act, which proposed letting holidays fall on a Monday to give employees a three-day weekend. While there was little opposition to what was clearly a stellar idea, lawmakers were less enthused about switching Washington’s Birthday from February 22—which was celebrated beginning in 1879 and would now be moved to the third Monday of February—to the all-inclusive President’s Day. The holiday officially remained Washington’s, though some state and local governments use the President’s Day label.

So what happened to Lincoln? Shouldn’t the president who effectively ended slavery and helped win the Civil War be granted a calendar tribute to call his own? People have tried. In the 1870s, a shopkeeper and Lincoln fan named Julius Francis tried to rally lawmakers to acknowledge Lincoln. New York, along with a few other states, agreed, but Congress didn’t. At the time, the country was still divided, with the South bitter over Lincoln’s victory. Later on, individual states reserved a date for his birthday on February 12. By 1940, 24 states and the District of Columbia marked their calendars for Lincoln. But many, like California, allowed it to phase out. Another holiday so close to Martin Luther King Jr. Day in January and Washington's Birthday in February seemed like one too many.

So whether you call it Presidents Day, President’s Day, or Presidents’ Day—there seems to be no official apostrophe placement, likely because it’s actually not an official label—be aware that it’s really all about Washington. It’s also an excellent time to buy a mattress.

[h/t The Christian Science Monitor]